A DC arc furnace basically comprises a cylindrical side wall extending upwardly from the periphery of a circular hearth and having a roof on its top. At least one consumable arcing electrode depends from the center of the roof for forming an arc with a melt on the hearth. At least a portion of the hearth is electrically conductive throughout an area that is symmetrical with the arcing electrode axis. U.S. Pat. Nos. 4,228,314 and 4,324,943 disclose such an arc furnace. The electrode, side wall and hearth are symmetrical with respect to the electrode axis, and the DC power conductor connections for the hearth are likewise symmetrically positioned.
The arc academically should burn vertically in alignment with the electrode when DC power conductors are connected to the electrode and hearth connections to power the arc. Practically, this result is not achieved because the strong magnetic fields of the power conductors cause the arc to burn angularly with its arc flare directed destructively against the side wall.
The furnaces disclosed by the previously mentioned patents are of the rocking type having a removable roof and equipment for lifting the electrode and removing the roof when the furnace is rocked for tapping a melt formed in the hearth. Such a furnace can be used not only as a metal-oxide reduction furnace but also as a scrap melting furnace when using a solid electrode. For this type U.S. Pat. No. 4,403,328 discloses a DC power conductor connection system providing conductor symmetry not previously possible, preventing the power conductor magnetic fields from appreciably affecting the arc.
Non-rocking DC arc furnaces arc used when only the direct reduction of metal-oxide is required, and can be made basically as disclosed by the initially mentioned two patents but with a non-removable roof and without the roof-removing equipment mentioned by U.S. Pat. No. 4,403,328. A tubular consumable arcing electrode for feeding the metal-oxide to the hearth is required and tapping is via a side tapping port, the reduced melt continuously being produced by continuous feeding through the electrode.